In examination by a microscope, a subject to be examined is sandwiched with a cover glass and a slide glass, which is then placed with the cover glass facing an object lens. However, the mere sandwiching of a subject to be examined with two glass plates often does not allow later examination of the same subject. In order to solve this problem, an adhesive was proposed. This is called a sealing agent and is used to sandwich a slice of an observed object, having dimensions of micron order, between two glass plates and pressure it in the same state as examined so that it can be stored for an extended period.
One of well known sealing agents is Balsam. This is a natural product and, therefore, has a disadvantage that its composition and quality vary depending on a growing district, a degree of purification, preservation conditions, etc. For the above reason, synthetic polymeric adhesives have been tried as sealing agents. See, for instance, Taichiro Akiyama and Setsuko Ueno, Rinshokensa, November 1966.
An increasing number of subjects are subjected to microscopic examination in the fields of medical science, pharmacology, biology, agricultural science and technology.
Operation of filling an interstice between two glass plates with a thin sealing agent layer to fix them is conducted almost completely manually. However, it is becoming impossible with such manual operation to meet the increasing quantity and time demands. In order to solve this problem, a method of automatically preparing specimens for microscopic examination was proposed as seen in U.S. Pat. Nos. 4,146,414 and 4,203,797, wherein a film composed of a transparent substrate coated with an adhesive is automatically layered on a slide glass on which a few drops of an organic solvent, capable of swelling or dissolving the above adhesive, has previously been dropped and a subject to be examined has been placed. Thus, the aforesaid film has both the function of a traditional cover glass and the function of a sealing agent. This type of film is hereinafter called a cover film.
However, this cover film of a transparent substrate previously coated with an adhesive requires improvement to permit a user to stably use it any time and anywhere. That is, the cover film easily causes so-called blocking between an adhesive layer and the reverse side of the film, i.e., the substrate surface opposite to the adhesive layer, during storage in a form of a roll. Once the blocking occurs, the adhesive layer transfers to the reverse side of the film or the surface of the adhesive layer becomes uneven, so that satisfactory sealing required for microscopic examination is unattainable.
Further, a sealed specimen for microscopic examination is not always stored at normal temperature and humidity. Some countermeasure is, therefore, required to prevent peeling-off between the cover film and the slide glass or between the substrate of the cover film and the sealing agent layer, even if it is stored in a certain range of temperature and humidity.